Electronic timing device



Feb. 16, 1954 J. J. ENTWISLE 2,669,677

ELECTRONIC TIMING DEVICE Filed March 6, 1952 124 B7 A B-Z A! IPBQ 03 R5IP81 INVENTOR 4' circuited but completed on depression of the PatentedFeb. 16 1954 UNITED STATES PATENT OFFICE ELECTRONIC THWING DEVICE JamesJ ohnstone Entwisle, Ormskirk, England Application March 6, 1952, SerialNo. 275,194

Claims priority, application Great Britain September 20, 1951 4 Claims.1

- curately defined intervals, the length of the interval beingadjustable.

One object of the invention is to provide such a device which will giveconsistent results over a wide range' of time-intervals, suchconsistency being an essential consideration in many photographicprocesses, especially those concerning the art of colour photography.Further objects of the invention are to provide a simple, robust andcompact unit, with a minimum of controls, and one which is not affectedby momentary variations of the electrical supply to which it isconnected. An essential feature of the device is that it is suitable foruse with existing photographic apparatus without modification of suchapparatus or the device. Its construction is such that moving parts areeliminated,- making the assembly more reliable, and continual use notaffecting its accuracy.

According to the present invention there is provided an electronictiming device including a control circuit fed by a source of alternatingcurrent, said control circuit comprising a vacuum tube having an anode,a cathode and at least one grid, a relay and a condenser in paralleltherewith, the winding of said relay being connected directly to saidcathode, contacts carried by said relay and operable by said relay onenergisation thereof to open to break a circuit to a load device, acapacitance-resistance circuit comprising a series-connected condenserand resistance and a further condenser connected in parallel with saidseries-connected condenser and resistance, a variable resistanceconnecting said capacitance-resistance circuit to said cathode and inparallel with said relay, a grid resistance connecting said variableresistance, on the capacitance-resistance circuit side thereof, to thecontrol grid, and means for momentarily short-1.

circuiting said relay together with its associated condenser and saidcapacitance-resistance circuit.

The means for momentarily short-circuiting said relay with itsassociated condenser and said capacitance-resistance are common and mayadvantageously be constituted by a single spring loaded push buttonswitch, normally open A further feature of the invention is that inorder to extend the time range of the device, a further resistance andcondenser in series are connected in parallel across the first-mentionedcapacitance-resistance circuit. By provision of a switch whereby thisfurther resistance can be short-circuited or included in the circuit atwill, the effective capacitance of the circuit may be altered, sopermitting a double range scale to be associated with the manual controlof the variable resistance, and increasing the time range ofthe device.

The invention will be described further, byway of example, withreference to the accompanying drawing which is a circuit diagram of anelectronic timing device according to the invention.

In the circuit diagram VA a suitable vacuum tube, for instance a highfrequency pentode of the type known under the designation 6SI-I7; LA isa lamp; RI, R2, R3, R4, R5, R6 and R1 are resistances havingrespectively ohmic values of 10,000 100,000, variable magnitude withmaximum 500,000, 100,000, 10,000, 10,000 and 500,000; Cl, C2 and C3 arecondensers having capacities of 10, 2 and 2 micro-farads respectively;SWI is a switch PBIPB2 are the poles of a spring loaded finger-operateddouble pole push button switch and A is a relay having spring restoredbreak contacts Al, i. e. contacts which normally are closed, but whichopen on energisation of the relay A. The circuit is fed by a source S ofalternating current, at 240 volts and cycles per second, for whichvoltage and frequency all the above-mentioned values of resistance andcapacitance are calculated in operation, when the source of supply S isswitched on, as by the usual type of toggle switch (not shown in thedrawing) the lamp LA, which is connected across the source S through therelay contacts Al is supplied directly with current since the relay A isnot operated and contacts Al are normally closed. The heatercircuit ofthe vacuum tube VA, containing a suitable series condenser C, is alsoconnected directly across the supply S, the condenser C presenting animpedance such as to provide for the correct operating voltage acrossthe tube filament F, and the tube filament F will warm up. As thecathode K is heated by the filament F, the tube VA commences to conductflowing through relayA to the correct value), which combination isitself connected in seriesin an operated condition). 7 will thereforeclose and reconnect the supply S with the cathode K. The potential dropdeveloped across the combination A and R6 will cause the condenser CI tocharge until eventually a steady state is reached when the tube VApasses sufficient current to maintain condenser Cl charged at a voltageadequate to cause relay A to operate. The desired steady state, however,will not be achieved until the condensers C2 and C3 have also beencharged, via the variable resistance R3, and again by the potentialdeveloped across relay A and resistance R6. On. operation of relay A,contacts AI will open 'to interrupt the supply S, and the lamp LA willbe extinguished.

The device is now ready for use and the manual control of variableresistance R3 is adjusted by reference to a previously calibrated scaleassociated with such control, thus adjusting the time constant of thecircuit including condensers C2, C3 and resistances R3, R! (if not inshort circuit by switch SWI), and hence settin the desired time intervalfor which the lamp subsequently is to remain alight. The scale may becalibrated in the required time units by predetermining the values ofcondensers C2 andCt at the minimum value of resistance and withresistance R? short circuited. These values of C2 and C3 will thendetermine the minimum time constant of the circuit including Cl, C2, C3,R3, A and R6 to determine theminimum time delay required for rechargingthe said condensers and hence re-operating relay A to extinguish thelamp LA. This time constant may be increased, and lamp I lit for alonger period by increasing the value of variable resistance R3 asrequired.

To operate the device, the push button of. switch PB|PB2 is depressed,thuscausing condensers C l, C2 and C3 simultaneously to beshortcircuited through limiting or spark quenching resistances R4 and R5and the said condensers thus become fully. discharged. The relay A willconsequently release since the holding potential previously supplied bycondenser Cl is removed, as also is the;potentialsimilarly appliedacross relay A by condensers C2 and C3 (which potential is in any caseinsufiicient, due to the small capacities of C2 and C3, to maintain therelay Relay contacts Al across the lamp LA, which will light. The pushbutton of switch PEI-P132 is immediately released and the lamp LA willremain illuminated for a set interval during recharging of the'condensers Cl, C2, C3, before being extinguished on re-operation ofrelay A. This'cycle isrepeated oneach depression of the push button ofswitch I justed to a large value, the condenser C! will not chargequickly for two reasons:

(a) The control grid GI of the tube will be i negatively biased relativeto the cathode due to the grid-leak resistance presented by R2 and R3.

This results in a reduced tube current and consequently a longercharging time for condenser Cl. In this connection. it maybe noted thatwhen the push. button of swit'cli"EBl'PB2 is 4 closed to discharge thecondensers Cl, C2 and C3, the provision of grid resistance R2 willprevent the tube VA from drawing an excessive current.

(in) If variable resistance R3 has any substantial value and/or if theresistance R1 is not short-circuited by switch SW1, the time constant ofthe circuit including condensers C2, C3 and resistance R! is increasedso that 'a longer period is required to charge this circuit andconsequently a longer period is required before the voltage developedthereacross becomes effective to'as'sist condenser CI to hold the relayA in an operated condition.

Resistance R1 may be included or not, as deshed, and in increasing thetime constant of the circuit including C2, C3, R'l, enables the timerange of the device to be rendered more extensive by the use of afurther calibrated scale associated with the manual control of variableresistance R3. Preferably the value of R1 is chosen such that theminimum time constant of the circuit including Cl, C2, C3, R3, R6,.R1

and relay A is equal to or just less than the maximum time constant ofsaid circuit when R! is .short-circuited.

A timing device constructed as .described is capable of operatingconsistently at time intervals of from one-fifth of a second up to asmuch as thirty or forty seconds.

The vacuum tube used, may in addition to the the control grid GIdescribed have, in known manner, a screen grid G2 externally directlyconnected to the anode A and a suppressor grid G3 directly connected tothe cathode K. The normal anode load and other resistance such as anodeload resistance RI, may be provided to ensure that the vacuum tubeoperates under the conditions recommended by the manufacturers thereof.

I claim:

1. An electronic timing device including a corntrol circuit fed by asource of alternating current, said control circuit comprising a vacuumtube having an anode, a cathcee and at least one grid, a relay and acondenser in parallel therewith, the of said relay being connecteddirectly to said cathode, contacts carried by said relay nd operable bysaid relay on energi'sation thereof to open to'b'realr a circuit to aload device, a capacitance-resistance circuit comprising a serice-connected condenser and resistance and a further condenserconnected in parallel with said series-connected condenser andresistance, a variable resistance connecting said capacitanceresistancecircuit to said cathode and in parallel with said reiay, a gridresistance connecting said variable resistance, on thecapacitance-resistance circuit side thereof, to the control grid, andmeans for momentarily short-circuiting said relay together with itsassociated condenser and said capacitance-resistance circuit.

2. An electronic timing device including acontrol circuit fed by asource of alternating current. said control circuit comprising a vacuumtube having an anode, a cathode and at least one grid, a relay and. acondenser in parallel therewith, the winding of said relay beingconnected directly to said cathode, contacts carried by said relay andoperable by said relay on energisation thereof to open to break acircuit to a load device, a capacitance-resistance circuit comprising aseries-connected condenser and resistance and a further condenserconnected in parallel with said. seriesconnected condenser andresistance. avariable resistance connecting said capacitance-resistancecircuit to said cathode and in parallel with said relay, a gridresistance connecting said variable resistance, on thecapacitance-resistance circuit side thereof, to the control grid, andmeans for momentarily short circuiting said relay, common to both thesaid relay with its condenser and to said capacitance-resistancecircuit, said means comprising a single spring loaded double pole pushbutton switch, connected so as on operation of said switch to shortcircuit said relay together with its associated condenser and saidtance-resistance circuit.

3. An electronic timing device including a corn trol circuit fed by asource of alternating current, i-

said control circuit comprising a vacuum tube having an anode, a cathodeand at least one grid, a relay and a condenser in parallel therewith,the winding of said relay being connected directly to said cathode,contacts carried by said relay and operable by said relay onenergisation thereof to open to break a circuit to a load device, acapacitance-resistance circuit comprising a series-connected condenserand resistance and a further condenser connected in parallel with saidseriesconnected condenser and resistance, a variable resistanceconnecting said capacitance-resistance circuit to said cathode and inparallel with said relay, a grid resistance connecting said variableresistance, on the capacitance-resistance circuit the resistance of saidcapacitance-resistance circuit so that it can be included in or removedfrom said capacitance-resistance circuit at will.

4. An electronic timing device including a control circuit fed by asource of alternating current, said control circuit comprising a vacuumtube having an anode, a cathode and at least one grid, a relay and acondenser in parallel therewith, the Winding of said relay beingconnected directly to said cathode, contacts carried by said relay andoperable by said relay on energization thereof to open to break acircuit to a load device, a capacitance-resistance circuit comprising aseries-connected condenser and resistance and a further condenserconnected in parallel with said seriesconnected condenser andresistance, a variable resistance connecting said capacitance-resistancecircuit to said cathode and in parallel with said relay, a double rangesuitably graduated scale associated with said variable resistance forindicating the various settings thereof, a grid resistance connectingsaid variable resistance, on the capacitance-resistance circuit sidethereof, to the control grid, and means for momentarily short-circuitingsaid relay together with its associated condenser and saidcapacitance-resistance circuit.

JAMES JOHNSTONE EN'IWISLE.

References Cited in the file of this patent UNITED STATES PATENTSDahline Aug. 14,

